a few months back I had placed blackout curtains in the bedrooms. With the temps falling below 0 some nights, I have invested in more of these for other rooms. I bought the Eclipse Blackout curtains. This was the lowest grade of the 3 types. http://www.walmart.com/ip/Eclipse-Samara-Blackout-Energy-Efficient-Curtain/15734048
My kitchen window over the sink was the worse, would develope ice on the inside after I did dishes. Not anymore since I replaced the curtain.